A conventional spark plug includes an insulator core assembly and an outer shell. A firing electrode extends from the insulator core assembly and a ground electrode extends from the outer shell, with the two electrodes being positioned to define a spark gap. When the spark plug is mounted in an engine, the spark gap is located in the combustion chamber of the engine. The firing electrode, also referred to as the center electrode, extends through a bore of the insulator core assembly and is part of a conduction path between a terminal at one end of the insulator core assembly and the spark gap at the other end.
In the combustion chamber, the pressure varies significantly during operation of the engine. The efficiency of the engine is reduced if there are pressure leaks in the combustion chamber. The spark plug may cause a pressure leak if a good seal is not provided between the center electrode and the insulator core. Conventionally, such a seal may be formed by tamping a powder in the bore between the insulator core assembly and center electrode, or by melting glass particles in the bore.